is this a turbo charged engine also?
I have taken off with a DA of 8800 ft, full rich and not had a problem in my
T-arrow
I use full rich on take off and landing, as my POH says to do.

Peter Duniho wrote:
My airplane, with a Lycoming TIO-540, will do the same thing at high

altitude airports if the mixture is set full-rich prior to touchdown.

Operationally, I simply leave the mixture alone during descent. Given that
descents are usually made at reduced power, theoretically I could even lean
the mixture during the descent (opposite of what you'd normally do with a
normally aspirated engine at power settings near cruise), but I just keep an
eye on the turbine inlet temperature and normally no change in mixture
setting is required to keep the TIT in the ballpark of 1500 F.

During a go-around, it is critical that I remember to push the mixture
full-rich, but since it is just as critical that the engine not stop until I
am actually done flying the airplane, this is an acceptable trade-off.

I also need to keep the mixture lean while taxiing, otherwise I get fouled
plugs. I asked my mechanic about both issues (since they seem related) and
he verified that the idle mixture is correct for my installation. It just
runs rich at or near idle power unless the mixture is manually adjusted. At
higher density altitudes, idle mixture is so rich it will flood the engine
and make it stop.

[...] Later that day, when taxiing for takoff, we set 1200 rpm
and leaned for peak rpm, mixture knob was out 1.5-2 inches to achieve
this.

I assume you mean you just did this as a test during taxi, and that you
returned the mixture to full rich before takeoff?

When we returned home to 800' elevation, we checked the idle speed at
full rich, it was about 500 rpm, is this too low?

Sounds about right, but I don't know the specifics for that engine. It
might be that it's supposed to be higher. I would ask the mechanic
maintaining the aircraft if he has the engine manual for the engine
installed, and then you can read in that what the actual numbers should be.

Pete